This error implies that the mailformatting_php.php include is below the WA_Email.php include. It looks like the issue is with aa-navbar4.php. Can I see a copy of that page?
Maybe try adding this:
<?php require_once("../webassist/email/WA_Email.php"); ?>
above the other includes on the page.php page. That way the aa-navbar4.php page won't try to add it below.